Philippines

Geology and tectonic evolution of Palawan – northern Borneo region

The island of Palawan, the most westerly island of the Philippine Archipelago, lies approximately 400 km to the northeast of northern Borneo along the southern margin of the South China Sea. On a broad scale these two areas — northern Borneo and Palawan — share many geological and physiographic characteristics.

Geologically, both areas are underlain by a complex basement of continental rocks overthrust by Mesozoic ophiolitic rocks that are intruded by young granitic plutons: the Late Miocene Mt Kinabalu pluton of northern Borneo and the Mt Capoas intrusion of Palawan. Physiographically, both onshore regions share a strong NE-SW orientation, are flanked to the west by significant bathymetric troughs and – in-turn – by bathymetric highs.
These shared geological and physiographic characteristics result from a common tectonic history that is linked to the opening of the South China Sea during the Early Cenozoic. Tectonic activity in northern Borneo culminated in the Early Miocene Sabah Orogeny, when continental fragments rifted from the South China margin and collided with the existing land mass. A similar scenario has been proposed for Palawan – material rifted from the South China margin is suggested to have collided with the Cagayan Ridge Arc in the Middle Miocene.Northern Borneo is known to have experienced significant uplift and erosion during the Miocene and Pliocene. It is suggested that this event is of regional significance, and that widespread uplift and erosion at this time created a large emergent landmass that encompassed both northern Borneo and Palawan.